Progressing cavity pumps made from helical gear pairs have been known since their invention disclosed in U.S. Pat. No. 1,892,217, entitled "GEAR MECHANISM" to Moineau. These pumps are comprised of two helical gears, one inside the other. The gears are engaged with each other along a sealing line to create cavities which progress axially as one of the gear pair is rotated relative to the other. According to Moineau's teaching, the outer gear has one more helical thread than the inner gear. Helical gear pair progressing cavity pumps in which the inner gear has one more thread than the outer gear are taught in U.S. Pat. No. 3,512,904, entitled "PROGRESSING CAVITY HELICAL PUMP" to Allen. Either gear design will hereinafter be referred to as a Moineau pump. The gear pair of a Moineau pump is subject to extensive wear because of the sliding contact required to create progressing cavities between the gear pair. This frictional contact causes wear which necessitates frequent replacement of one or both gears. Commercially available Moineau pumps, as well as those disclosed in the prior art, require extensive disassembly of the pumping apparatus to replace the worn gear pair.
In addition to the gear pair, Moineau pumps require other moving parts because of relative gear movement. As one of the gear pair is rotated relative to the other, the centerline of one gear is also required to orbit or gyrate relative to the centerline of the other gear because of the basic geometry of the gear pair. This combination of movements is accommodated in the prior art by three basic approaches, but each approach requires that moving components other than the gear pair come in contact with the pumpable material. This contact is undesirable not only because of maintenance costs, but, in many instances, the pumpable material is corrosive, abrasive, explosive or otherwise incompatible with long term safe use of the pump in its intended application. Inspection and maintenance of these mechanical components as well as inspection, maintenance and replacement of the helical gear pair is a major cost of operating this type of pump.
One method to accommodate the movement of the gears relative to each other revealed in the prior art is to fix the outer gear of the pair and rotate the inner gear with a drive shaft. Thus, the inner gear orbits or wobbles while rotating. Various types of universal joints, flexible shafts and mechanical connections employing this first approach are disclosed in U.S. Pat. No. 2,028,407, entitled "GEAR MECHANISM," to Moineau; U.S. Pat. No. 3,567,340, entitled "SCREW PUMP PROVIDED WITH A RADIALLY MOVABLE ROTOR COUPLING," to Benson; U.S. Pat. No. 4,599,056, entitled "UNIVERSAL JOINT AND PROGRESSIVE CAVITY TRANSDUCER USING THE SAME," to Crase; U.S. Pat. No. 4,153,397, entitled "ROTOR DRIVE COUPLING FOR PROGRESSING CAVITY PUMP," to Allen; U.S. Pat. No. 4,140,444, entitled "FLEXIBLE SHAFT ASSEMBLY FOR PROGRESSING CAVITY PUMP," to Allen; U.S. Pat. No. 4,080,115, entitled "PROGRESSIVE CAVITY DRIVE TRAIN," to Sims et al.; U.S. Pat. No. 4,237,704, entitled "OLDHAM TYPE COUPLING AND PUMP EMBODYING THE SAME," to Varadan; and U.S. Pat. No. 4,591,322, entitled "ECCENTRIC ARCHIMEDIAN SCREW PUMP OF ROTARY DISPLACEMENT TYPE," to Ono et al.
Teachings of these patents and other means known in the prior art for permitting the rotary driven Moineau gear to freely align itself engagingly with the other gear of the Moineau pair will be referred to herein as a flexible rotary drive coupling.
A second arrangement revealed in the prior art to provide for the relative motion of the Moineau gear pair is to rotate one gear of the pair about a fixed axis and mount the nonrotating gear in a manner to permit it to wobble, orbit or gyrate relative to the rotating gear. Four different disclosures are taught in U.S. Pat. No. 2,505,136, entitled "INTERNAL HELICAL GEAR PUMP," to Moineau; U.S. Pat. No. 2,527,670, entitled "HELICAL PUMP," to Allen; U.S. Pat. No. 2,612,845, entitled "HELICAL GEAR PUMP WITH NONRIGID CASING," to Byram et al.; and U.S. Pat. No. Re. 29,180, entitled "MOINEAU PUMP WITH ROTATING OUTER MEMBER," to Clark. Clark teaches a method of securing the inner gear to prevent it from rotating while permitting it to wobble as the outer gear is rotated about its own axis. The embodiment of this disclosure, however, does not have sufficient resistance to axial thrust forces imparted to the inner gear during operation to provide reliable operation. The Clark invention also requires multiple bearings and rotating seals which are contacted by the pumpable material. Bvram's disclosure teaches a one piece elastomeric outer gear that is flexible in its retention structure so that it will wobble relative to the inner gear even though attached to a non-wobbling mount. This type of outer gear is normally used as a stator and is referred to in the prior art as a wobble stator.
The third approach to accommodate the relative motion of the Moineau gear pair is to rotate the inner gear of the pair through one flexible joint and mount the outer gear flexibly so that the wobbling or orbiting is shared by both gears. This approach is disclosed in U.S. Pat. No. 2,532,145, entitled "PUMP," to Byram; U.S. Pat. No. 2,545,626, entitled "SPIRAL GEAR PUMP AND ALLIED DEVICE," to Moineau; and U.S. Pat. No. 4,325,682, entitled "APPARATUS FOR DISCHARGING MATERIALS," to Willis.
Prior art using these three approaches in all cases, except the last reference to Willis, requires that the moving joints, flexing connections, bearings and rotating seals be located within the pumping chambers, and again, these components must come in contact with the material being pumped. The invention by Willis teaches that only one flexing connection is in contact with the pumpable material, but Willis also requires a flexible process hose and extensive disassembly to replace the outer gear.
It is well known in the practice of this prior art that extended operating time before failure of components other than the helical pair is achieved by avoiding contact of the pumpable material with the moving joints, flexing connections and bearings. The prior art presents two arrangements whereby the pumpable material does not contact with these moving parts. First, the mechanical parts to be protected are sealed from contacting the pumpable material with a device that does not restrict the movement of the component being protected; and secondly, the mechanical part to be protected is located on the exterior of chambers containing the pumpable material. Examples of sealing means invented to protect moving mechanical parts from contact with the pumpable material are U.S. Pat. No. 4,639,200, entitled "SEALING APPARATUS FOR A GEAR BALL JOINT," to Baumbardner et al.; U.S. Pat. No. 2,915,979, entitled "GRIT AND CORROSION SEAL FOR UNIVERSAL JOINTS IN PUMPS HAVING ECCENTRICALLY MOVING ROTORS," to Bourke et al.; and U.S. Pat. No. 3,165,065, entitled "FLEXIBLE COUPLING FOR SCREW PUMP ROTORS," to Stickel. Such seals are effective in increasing pump operating time before component failure, but extensive disassembly is still necessary to replace the protected component when it does fail. The use of such seals, moreover, is not safe for use with pumpable explosive mixtures because of the potential explosion when the sealing component fails. Inspection of the seals to insure their integrity prior to failure is also costly and time consuming because of the elaborate disassembly required to view the seals and inspect or replace them. The second method to prevent contact between the pumpable material and certain moving parts involves locating flexible joints to the exterior of chambers containing the pumpable material, as taught by Willis in his previously mentioned U.S. Pat. No. 4,325,682; and U.S. Pat. No. 3,930,765, entitled "ROTARY DISPLACEMENT PUMPS," to Waite. These methods avoid contact of the pumpable material with the components located external of the pumping chambers and also provides for inspection and maintenance of these components without pump disassembly. Nonetheless, at least one flexing or rotating seal does come in contact with the pumpable material. Replacement of the helical gear pair, moreover, requires extensive disassembly and disconnection from processing equipment or piping.
Hollow inner gears as well as closed end outer gears are known in the prior art. For example U.S. Pat. No. 2,525,265 to Moineau and U.S. Pat. No. 3,746,310, entitled "VIBRATOR DRIVEN BY PRESSURIZED FLUID" to Fransson et al. Moineau '265 discloses the use of multiple gear pairs to construct a glandless pump. Embodiment of the disclosure requires a complexity of bearings for rotating and sliding components as well as rotating inner gears. Disassembly and repair is made more complex by the required arrangement and many catch points for contamination are created. Fransson et al. '310 teaches a rotating and orbiting inner gear, but the device has no provision for attachment of a mechanical drive. Another hollow inner gear for fluid flow known to the prior art is disclosed in U.S. Pat. No. 4,614,232, entitled "DEVICE FOR DELIVERING FLOWABLE MATERIAL" to Jurgens et al. In this disclosure fluid flow through a hollow stationary inner gear creates rotation and orbiting of an outer gear. The outer gear also serves as the inner gear of a second Moineau gear pair. A rotating seal is required to close one end of the rotating and orbiting gear and there is no provision for connection of a rotary drive.
The prior art does not reveal the novel combination of a closed end outer gear rotatably driven about a nonrotatable hollow inner gear adapted for fluid flow through the inner gear. The present invention represents a new and useful improvement in Moineau gear pairs and it makes possible realization of the objectives of the invention.